Field of Invention
The present invention is in the field of devices or apparatus for detecting and logging incidents of ferromagnetic objects in or on personnel and equipment in the vicinity of an operating magnetic resonance imaging (MRI) device.
Background Art
The large magnetic field of the MRI magnet will attract ferromagnetic objects in the MRI magnet's field of influence. This force of attraction can cause ferromagnetic objects to approach the MRI magnet at high velocity. The force of attraction is related to the product of the magnetic field spatial gradient (dB/dz) and the magnetic field strength B. Modern MRI machines, which have large magnetic fields and steep spatial gradients, can impart a strong force on relatively modest sized objects. It is known, for example, that a hairpin can reach speeds of 40 MPH when released near a typical 1.5 Tesla MRI.
The risk and consequent injuries from a projectile attracted are well known. In 2001, for example, a 6 year old boy was killed when a ferromagnetic oxygen cylinder was pulled into the magnet while he was being imaged. But even small objects can be dangerous. For example, an MRI patient needed to have a bobby pin surgically removed from the nasal cavity when the pin was drawn towards the center of the bore while the patient was laying head-in in the MRI. Another MRI patient forgot a fingernail clipper was in his pocket. While in the MRI magnet, he tried to remove it. The fingernail clipper slipped from his hands, and flew into his eye causing blindness. There are also life threatening risks to patients and other personnel who have implanted devices such as pacemakers, implanted defibrillators, or intracranial aneurysm clips.
Ferromagnetic metal detectors provide a means to detect ferromagnetic objects. U.S. Pat. No. 7,489,128, issued Feb. 10, 2009 to Kopp, discloses a special type of Ferromagnetic metal detector that is capable of being located at the doorway of an operable MRI apparatus. The apparatus is capable of providing an alarm to help protect personnel from the problem of ferromagnetic objects knowingly or negligently being brought into the MRI magnet room.
However, with over 20,000,000 MRI scans performed in the U.S. annually, the use of a Ferromagnetic metal detector alone may not be sufficient to reduce the occurrence rate of projectile related incidents in the MRI room. Indeed, analysis of the reports in the Food and Drug Administration MAUDE incident reporting data base indicates that the rate of projectile incidents exceeds the rate of increase in the number of MRI scans performed.
An effective technique to reduce the occurrence rates of incidents in the hospital environment and elsewhere is the application of root cause analysis (RCA). RCA was used to analyze the events which led up the previously described incident where a 6 year old boy was killed by an oxygen cylinder. In this incident, there were a number of participants and witnesses to the events leading up to the final tragedy. As a result, there was sufficient data to detail the actions which occurred.
A Blue Ribbon Committee appointed by the American College of Radiology (ACR) made a number of recommendations based, in part, on the RCA of the above incident. The ACR in a White Paper indicated the MRI magnet room should be isolated so that the general public and untrained medical personnel will not have access to the projectile risk associated with the strong magnetic field contained in the MRI magnet room.
This recommendation of limiting access to the MRI magnet room has had a positive affect by reducing inadvertent access to a potentially dangerous area. However an unintended consequence, of the restriction of access to the magnet room area is that an effective RCA cannot be performed since, in many cases there are no impartial witnesses to the sequence of events leading up to the projectile incident. There have been a number of reported incidents where only the victim was present at the time of the incident.
As can be appreciated, continued improvements are needed. For example, it would be beneficial to provide an automatic method to allow the independent documentation of incidents to allow corrective actions as well as RCA to be performed.